Driving and positioning system

ABSTRACT

A driving and positioning system consisting of a rotor equipped with  permnt magnets and of a stator with at least two windings. The windings are connected to an electronic voltage-supply circuit controlled by rotor-position sensors for commutating the current. To improve its adjustment potential by converting the system into one that can be magnetically meshed or latched, the stator is non-ferrous, the disk-shaped stator windings, which are positioned in parallel planes, are overlapped in such a way that the magnetic field generated by the windings and surrounded by the coils is essentially parallel to the magnetic field generated by the permanent magnets, and the rotor-position sensors are each integrated into both windings. A practical electronic voltage-supply circuit for controlling the system is also described. It has two sets of multiplication stages and a set of addition stages in a prescribed layout.

This application is continuation of application Ser. No. 828,118, filed2/10/86 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a driving and positioning systemconsisting of a rotor equiped with permanent magnets and of a statorwith at least two windings, whereby the windings are connected to anelectronic voltage-supply circuit controlled by rotor-position sensorsfor commutating the current.

A driving and positioning system of this type is described in a 1978brochure issued by the firm of Magnetic Technology, in which it iscalled a brushless DC motor. The motor is intended for variousapplications. It has a permanent-magnet rotor and a plated stator with astator winding that consists of two windings. Appropriately positionedrotor-position sensors, which can be Hall sensors, determine the actualrotor position at any instant. The electronic voltage-supply circuitcommutates a feed current obtained from two power amplifiers to the twocoils depending on the particular rotor position detected in such a wayas to produce a continuous rotation.

The effects of hysteresis in the iron circuit of the stator in such amotor and the relatively high electric time constants diminish theprecision that the movement of rotation can be adjusted to make itdifficult to maintain a prescribed reference position. The motor alsoexhibits saturation and eddy-current phenomena in the soft iron as wellas preferred mechanical rotor zero positions, leading to alternating-and direct-current losses.

Also state of the art is the brushless direct-current motor with no ironin the stator described in "A high-speed high-efficiency permanentmagnetic motor-generator" by A. R. Miller, published in June 1978 by theLincoln Laboratory, MIT, Lexington, Mass. As the rotor, equipped with anumber of sector-shaped permanent magnets, rotates, it induces signalvoltages in the stationary stator winding. The voltages are employed tocommutate the stator current in an electronic voltage-supply circuit.This brushless motor as well makes it possible to obtain only dynamiccommutation during rotation, but not to establish a desired staticreference position.

German Patent Application No. 2 832 387 discloses a direct-current motorwithout a collector and with an axial air gap. It has axially magnetizedpermanent magnets mounted on a rotor plate and magnetically connected toa rotor back-connection plate. The stator consists of two star-shapeddrive coils superimposed like disks and positioned on a stationaryback-connection plate that can be magnetized. The rotational-positiondetector consists of two Hall generators. The stationary andmagnetizable back-connection plate constitutes not in a non-ferrousstator, whereas there are magnetizable materials present in thealternating magnetic field.

DD Patent No. 34 431 describes a flat and slow motor intended fordirectly driving flywheel masses. The stator has several flat, rathertrapezoidal coils. There are no rotor-position sensors. An electronicswitch can be employed as a commutator, controlling the stationary coilsone after another at a prescribed rate. The current can alternatively becommutated by a collector in conjunction with slip and segment rings.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a driving andpositioning system appropriate for a wide range of applications,especially at low temperatures, and allowing low-loss establishment ofany desired reference angles of rotation, which will be as unlimited asdesired and extremely stable. The system shall also maintain anyprescribed reference position with high precision, consume no energy inthat position, and emit maximum torque at even slight deviations fromthe reference position, which may be a rest position or a position thatoccurs during rotation. The system shall also allow high speeds at lowloss.

This object is attained in accordance with the invention in a drivingand positioning system of the aforesaid type wherein the stator isnon-ferrous, wherein a disk-shaped stator windings I and II, which arepositioned in parallel planes, are overlapped in such a way that theempty spaces inside the coils are all completely occupied by webs onother coils, whereby the magnetic field generated by the windings andsurrounded by the coils is essentially parallel to the magnetic fieldgenerated by the permanent magnets, and in that the rotor-positionsensors are each integrated into both windings I and II.

A system of this type, which does not involve iron in the stator, willmake it possible in conjunction with an appropriate electronicvoltage-supply and voltage-control circuit to position the rotorprecisely at any desired reference angle β of rotation. It will bepossible to precisely establish the reference position with a powerfulretentive force even after a prescribed rest position is arrived at. Therotor will behave as it rotates and in its established referenceposition practically as if magnetically meshed or latched, and everydeviation from the prescribed in-motion or at-rest position willencounter powerful magnetic forces. The aforesaid non-ferrous designwill allow extremely precise and low-loss control and provide poweruptake that depends only on the deviation from the reference value.

Rotor-position sensors are sensors that generate signals that depend ona magnetic field. It is preferable to employ sensors that determine notonly the magnitude but also the sign of the magnetic field and releaseelectric output signals.

It can also be practical for the rotor-position sensors to be Hallsensors, which are in themselves known, resulting in beneficial inputparameters for the electronic voltage supply and control circuit.

It is practical to provide more rotor-position sensors than windings Iand II. There should be rotor-position sensors not only to allow thecommutation but more than these to detect the position of the rotor andthus to provide additional rotor-motion parameters that can be processedfor use in a control circuit. Since two windings make it possible toobtain the desired information with a minimum of two rotor-positionsensors, there will be at least as many sensors as windings. In designswith more than two windings, however, the requisite signal values can beobtained with as many sensors as, or with less sensors than, there arewindings.

One preferred embodiment of the invention employs four rotor-positionsensors in conjunction with a stator winding consisting of two windingsI and II and displaced by an angle π/2n, wherein n is the number ofpairs of poles generated by the permanent magnets and determining theair gap that the stator windings I and II are positioned in.Specifically, the angular displacement equals (1+4 m)·π/2n, wherein m=0,1, 2, 3, . . . can assume any whole-number value.

The opposing pairs of poles at the air gap can be generated by differentmeans, especially by opposing disk-shaped permanent magnets or by thepole shoes of an iron circuit that contains one or more permanentmagnets.

With respect to design it seems to be practical for the rotor to be anannular ferromagnetic support with a U-shaped cross-section and with anumber of pairs of poles generated by the permanent magnets anddetermining the air gap that the stator windings I and II engagepositioned on the opposing inner surfaces of its legs.

In this case it is practical for U-shaped cross-section of the supportto have annular surfaces that face each other and are coaxial to theaxis of rotation or cylindrical surfaces that are concentric with theaxis of rotation. Designing the support with parallel annular surfacesresult in a system that is compact, which is practical for variousapplications.

Although a system of the overall type just described can be combinedwith various types of electronic voltage-supply circuits, the circuitthat will now be described seems to be especially practical,facilitating unobjectionable magnetically meshed or latched motion onthe part of the rotor and precise establishment of prescribed referencepositions.

An electronic voltage-supply circuit of this type can be practicallyconstructed for two windings in that the output signals U_(H).sbsb.1,U_(H).sbsb.2, U_(H).sbsb.2, and U_(H).sbsb.4 from at least tworotor-position sensors are supplied to associated multiplication stages₁, ₂, ₃, and ₄ where they are multiplied by signal values derived fromthe reference angle β of rotor rotation and in that the windings I andII are connected to associated power amplifiers L₁ and L₂ that havetheir inputs connected to other multiplication stages ₅ and ₆ that aresupplied with the output signals U_(H).sbsb.1 and U_(H).sbsb.2 from tworotor-position sensors and with further input signals that areconstructed by addition stages Σ₁, Σ₂, and Σ₃ out of the output signalsfrom the first multiplication stages ₁, ₂, ₃, and ₄.

One practically proven circuit employs four rotor-position sensors,displaced at an angle π/2n. A constant rotation of the rotor will yieldfor example a sinusoidal curve for the field that rotates along with thepairs of poles and field-proportional sinusoidal Hall-sensor signals,with each signal displaced at an angle π/4 from its predecessor. Thisresults in the signals from Hall sensors H₁, H₂, H₃, and H₄, dependingon the relative angle α of rotation, of

    U.sub.H.sbsb.1 =C·sin (nβ/2)

    U.sub.H.sbsb.3 =C·sin (nβ/2+π/4)

    U.sub.H.sbsb.2 =C·sin (nβ/2+π/2)

    U.sub.H.sbsb.4 =C·sin (nβ/2+3/4π)

where C is a constant numerical value.

The output signal from each of the four Hall sensors is supplied to anassociated multiplication stage, where it is multiplied by varioussignal values a, b, c, and d, which, as functions of reference angle βof rotation, have the dimensions

    a=cos (nβ/2)

    c=cos (nβ/2+π/4)

    b=cos (nβ/2+π/2)

    d=cos (nβ/2+3/4π)

As long as actual angle α of rotation differs from reference angle β ofrotation, therefore, the electronic voltage-supply circuit will supplyload currents in accordance with the direction of rotation through thepower amplifiers associated with the corresponding windings. Themagnetic field generated by the activated windings will attempt decreasethe control deviation.

Other appropriate elements can also be employed instead of Hall sensorsto detect the positions. Another design, in which rotor-position signalsare generated by a separate and additional system of permanent magnetsor by a different type of signal-generator system can also be employedinstead of sensing carried out by rotor-position sensors integrated intothe windings.

A system with a non-ferrous stator and disk-shaped stator windingspositioned in parallel planes will, in conjunction with the aforesaidelectronic voltage-supply circuit, unobjectionably position a componentthat is to be driven and that is connected to the driving unit, asupport for instance. Magnetically meshing or latching the rotor as itrotates enables powerful forces to be transmitted to the drivencomponent even at slow speeds or at rest, forces that will compel itspositioning within the prescribed time function of the reference angleof rotation.

Some preferred embodiments of the invention will now be described withreference to the attached schematic drawings, wherein

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a developed view of the rotor and stator winding representedas a function of angle α of rotation,

FIG. 2 is a graph with respect to time of the activity of theHall-sensor signals in FIG. 1 at constant rotation,

FIG. 3 is a block diagram illustrating how the Hall-sensor signals fromFIGS. 1 or 2 are processed,

FIG. 4 illustrates an embodiment in which the pairs of poles arepositioned on annular surfaces on the rotor, and

FIG. 5 illustrates an embodiment in which the pairs of poles arepositioned on cylindrical surfaces on the rotor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The top of FIG. 1 shows two mutually displaced windings I and II belowthe poles (X) and (•) of a rotor. Since windings I and II overlap in apractical way, the empty space inside the coils of one winding iscompletely occupied by the webs of the coils of the other winding. Theempty space inside the coils is accordingly exploited in a practicalway. Hall sensors H₁, H₂, H₃, and H₄ are integrated into the windings inthe positions indicated relative to the windings or to their coils. Thebottom of FIG. 1 shows the strength of the magnetic field generated bythe rotor poles, specifically in a static situation--at time t=0,resulting in Hall-sensor signals that correspond to the sinusoidal curveof field strength as a function of angle α of rotation.

FIG. 2 illustrates the dynamic situation with the rotor rotating atconstant speeds, each as the function of a particular Hall-sensor signalover time.

The block diagram in FIG. 3 illustrates how the Hall-sensor signals arefurther processed. The four Hall sensors H₁, H₂, H₃, and H₄ areconstantly supplied with current from a source I_(C). The fourHall-sensor signals U_(H).sbsb.1, U_(H).sbsb.2, U_(H).sbsb.3, andU_(H).sbsb.4 are appropriately amplified by downstream amplifiers V₁,V₂, V₃, and V₄ and supplied to multiplication stages ₁, ₂, ₃, and ₄,where they are multiplied by various signals a, b, c, and d in such away that signals a·U_(H).sbsb.1, b·U_(H).sbsb.2, c·U_(H).sbsb.3, andd·U_(H).sbsb.4 appear at the multiplication-stage outputs.

Signals a, b, c, and d are functions of prescribed reference angle β ofrotation and are generated from the functions sin (nπ/2) and cos (nπ/2)in such a way as to result in the equations

    a=cos (nβ/2)

    c=cos (nβ/2+π/4)

    b=cos (nβ/2+π/2)

    d=cos (nβ/2+3/4π)

The output signals from multiplication stages ₁, ₂, ₃, and ₄ are thenadded together in addition stages Σ₁, Σ₂, and Σ₃, and the total suppliedthrough a servo amplifier R to two other multiplication stages ₅ and ₆,which Hall-sensor signals U_(H).sbsb.1 and U_(H).sbsb.2 are alsodirectly supplied to. A signal that activates a power amplifier L₁connected to winding I is then constructed from the product ofU_(H).sbsb.1 and from the total signal from Σ₃ amplified in poweramplifier R. A signal that activates another power amplifier L₂ thatsupplies winding II is similarly generated through multiplication stage₆ as the product of Hall-sensor signal U_(H).sbsb.2 and the signal Σ₃amplified in servo amplifier R.

Amplifiers V₁, V₂, V₃, and V₄ should be stable, low-noise, and rapidproportional amplifiers. Servo amplifier R can be employed to determinethe effect of total output signal Σ₃ on each of the products to beconstructed in downstream multiplication stages ₅ and ₆.

The prescribed reference angle β of rotor rotation can be established ina reference generator SW as a function over time. In the simplest case,voltages corresponding to a specific reference angle can be tapped froma voltage divider.

For a single motion is β=f(t), and β(t)=2πνt for continuous rotation ata speed of 2ν/n, where ν is the frequency of oscillation of signals a,b, c, and d. Sin (nβ/2) and cos (nβ/2) are constructed in a computer Gfrom prescribed reference angle β of rotation and supplied to an addingamplifier Σβ and to a differential amplifier Δβ, which generate one ofthe input parameters of initial multiplication stages ₃ and ₄. Each ofthe other input parameters consists of a Hall-sensor signal U_(H).sbsb.3and U_(H).sbsb.4. Thus, aforesaid signals a, b, c, and d will be at theinitial inputs of initial multiplication stages ₁, ₂, ₃, and ₄. Theoutput signals from adding amplifier Σβ and differential amplifier Δβare cos (nβ/2+π/4) and cos (nβ/2+3/4π), specifically c and d.

The four Hall sensors in this circuitry sense the instantaneous localfield activity in relation to one coil of the windings and compare it toa theoretical reference curve obtained from reference angle of rotationβ. The electronic controls activate windings I and II in such a way thatboth curves coincide as much as possible in a state of equilibrium.Thus, actual angle α of rotor rotation will coincide with eachprescribed reference angle β, which can be a constant or a prescribedreference function with respect to time. Since the Hall sensors cansense with practically infinite resolution, any desired angle α of rotorrotation can be established with high resolution, and precisely guidedmotions can be carried out because, at the slightest deviation of actualangle α from an instantaneous reference angle β, a maximal torque willbe generated to readjust it.

Thus, the rotor will always be in an electrodynamically meshed orlatched state, with the particular position established and shiftedelectronically. Since the meshed position can also rotate at constantspeed, speeds that are as low as possible can be established at fulltorque. The electronic meshing or latching resulting from the specialnon-ferrous design of the system's coils in conjunction with theparticular electronic voltage-supply circuit far exceeds mechanicalmeshing or latching in precision, reproducibility, and life. Since therotor has no preferred mechanical zero position, electric power willessentially be consumed only when deflecting forces act from thereference position.

The absolute rotor position is initially dependent on the number ofpoles.

If the prescribed maximal torque is exceeded, the drive will disengageand can assume one of the other n/2 possible catch positions distributedaround the circumference. In applications in which this approach isimpermissible, absolute definition can be attained with additional knownmeans (identification and count-off of the meshing situations) or byinstalling a permanent-magnet system with n=2. The system can also beoperated like any other drive system in normal servo function by meansof external position indication as well as converted to ungoverned motoroperation. Combination with other analog or digital encoder is alsopossible.

FIGS. 4 and 5 illustrate two possible embodiments of the physicaldriving and positioning system. The ferromagnetic support for the rotor1 illustrated in FIG. 1 is in the form of a coil and supports twoannular disks 2 and 3 with permanent magnets that create a pair 4 and 5of poles mounted on its inner surface. A non-ferrous, stationary, anddisk-shaped stator winding 6 engages the air gap between pair 4 and 5 ofpoles and annular disks 2 and 3. Stator winding 6 has a cross-section inthe shape of an I and includes the coils, cast out of resin, of twowindings I and II along with Hall-sensor supports 7, which areadjustable in position. A shaft that is to be driven is directlyinserted in a central recess 8 in rotor 1, which it is connected to insuch a way that it cannot rotate relative to rotor 2. In the particularembodiment illustrated, a stop pin 9 secures annular disks 2 and 3 insuch a way that they cannot rotate.

The support illustrated in FIG. 5 has two concentric annular cylindricalsurfaces 10 and 11 that support a pair 4 and 5 of poles. The statorwinding 6 in this embodiment is also non-ferrous. It has a cross-sectionin the shape of a T, but cylindrical. Hall sensors 7, which areadjustable in position, are integrated into windings cast out ofartificial resin.

One essential feature of the invention is that the rotor-positionsensors are integrated into both windings, resulting in an especiallyfavorable shape for the signals generated in the rotor-position sensorsby the permanent magnets. In the present embodiment this is ensured byoverlapping the windings in parallel planes. This design also makes itpossible to position the sensors in relation to the windings in such away that the upstream effect of the windings on the position sensorsassociated with them by means of the electric control circuit remainsslight.

It will be appreciated that the instant specification and claims are setforth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:
 1. In a driving and positioning system having arotor with permanent magnets, a stator with at least two windings,rotor-position sensors, and an electronic voltage-supply circuitconnected to the windings and controlled by the rotor-position sensorsfor commutating the current to the windings, the improvement wherein thecircuit comprises amplifier means responsive to output signals from atleast two rotor position sensors, first multiplication stages formultiplying the output signals from said amplifier means by signalvalues derived from a reference generator, power amplifiers connected tosaid at least two windings, addition means for adding the output signalsfrom the first multiplication stages, second multiplication stages formultiplying the output signals from at least two rotor-position sensorswith the output signals from the addition means and wherein the outputsof the second multiplication stages are connected to the inputs of thepower amplifiers for controlling the commutation of said windings. 2.The system as in claim 1, wherein the circuit has four rotor-positionsensors displaced at an angle π/2n, where n is the number of pairs ofrotor permanent magnets.